Chemical-mechanical planarization ("CMP") processes remove material from the surface of a wafer or other substrate in the production of semiconductor devices. FIG. 1 schematically illustrates a CMP machine 10 with a platen 20, a wafer carrier 30, a polishing pad 40, and a planarization liquid 44 on the polishing pad 40. The polishing pad may be a conventional polishing pad made from a non-abrasive material (e.g., polyurethane), or it may be a new generation fixed-abrasive polishing pad made from abrasive particles fixedly dispersed in a suspension medium. The planarization liquid may be a conventional CMP slurry with abrasive particles and chemicals that remove material from the surface of the wafer, or it may be a solution without abrasive particles. In most CMP applications, conventional CMP slurries with abrasive particles are used on conventional polishing pads, and planarizing liquids without abrasive particles are used on fixed-abrasive polishing pads.
The CMP machine 10 also has an under-pad 25 attached to an upper surface 22 of the platen 20 and the lower surface of the polishing pad 40. In one type of CMP machine, a drive assembly 26 rotates the platen 20 as indicated by arrow A. In another type of CMP machine, the drive assembly reciprocates that platen back and forth as indicated by arrow B. Because the polishing pad 40 is attached to the under-pad 25, the polishing pad 40 moves with the platen.
The wafer carrier 30 has a lower surface 32 to which a wafer 12 may be attached, or the wafer 12 may be attached to a resilient pad 34 positioned between the wafer 12 and the wafer carrier 30. The wafer carrier 30 may be a weighted, free-floating wafer carrier or an actuator assembly 36 may be attached to the wafer carrier 30 to impart axial motion, rotational motion, or a combination of axial and rotational motion (indicated by arrows C and D, respectively).
To planarize the wafer 12 with the CMP machine 10, the wafer carrier 30 presses the wafer 12 face-downward against the polishing pad 40. While the face of the wafer 12 presses against the polishing pad 40, at least one of the platen 20 or the wafer carrier 30 moves relative to the other to move the wafer 12 across the planarizing surface 42. As the face of the wafer 12 moves across the planarizing surface 42, the polishing pad 40 and the planarizing solution 44 continually remove material from the face of the wafer.
One objective of CMP processing is to produce a uniformly planar surface on the semiconductor wafers. The uniformity of the planarized surface is a function of several factors, one of which is the distribution of abrasive particles between the wafer and the polishing pad. Fixed-abrasive polishing pads provide a substantially uniform distribution of particles between the wafer and the polishing pad because the abrasive particles are fixedly dispersed in the pad. CMP slurries with abrasive particles, however, may not provide a uniform distribution of particles because the slurry builds up at the perimeter of the wafer leaving less slurry under other parts of the wafer. Thus, it is desirable to use fixed-abrasive polishing pads.
One problem with using fixed-abrasive polishing pads to remove material from the surface of the wafer is that the fixed-abrasive pads tend to have a relatively low polishing rate compared to conventional pads and slurries. Fixed-abrasive pads are often used without a slurry because conventional planarization slurries with abrasive particles damage the planarizing surface of fixed-abrasive polishing pads. For example, when a wafer is planarized on a fixed-abrasive pad with a conventional abrasive slurry, the abrasive particles in the slurry generally damage the abrasive particles of the polished pad. Thus, it would be desirable to increase the polishing rate of fixed-abrasive pad CMP without damaging the fixed-abrasive pad.
Another problem with fixed-abrasive pad CMP is that defects may accidentally form on the surface of the wafer. As material is removed from the wafer, abrasive particles and other parts of the fixed-abrasive polishing pad may break away and become trapped between the surface of the wafer and the fixed-abrasive polishing pad. When the fixed-abrasive pad is used without a slurry, the detached pieces of the fixed-abrasive polishing pad often scratch the wafer and may damage several die on the wafer. Therefore, it would also be desirable to reduce defects caused by fixed-abrasive polishing pads.